The present application relates to head-mounted display apparatuses to be worn on heads of observers.
There are some virtual-image display devices (image display devices) each enabling an observer to observe a two-dimensional image formed by an image-forming device in a form of a virtual image enlarged by a virtual-image optical system, as disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2006-162767.
FIG. 8 is a conceptual diagram of an exemplary image display device 100. The image display device 100 includes an image-forming device 111 having a plurality of pixels arranged in a two-dimensional matrix, a collimating optical system 112 collimating light emitted from the pixels of the image-forming device 111 into parallel light, and an optical device (light-guiding means) 120 receiving the parallel light from the collimating optical system 112, guiding the light therethrough, and outputting the light. The image-forming device 111 and the collimating optical system 112 constitute an image generator 110. The optical device 120 includes a light-guiding plate 121 causing the received light to propagate with total reflection thereinside before outputting the light, first deflecting means 130 (for example, a layer of light-reflecting film) reflecting the light received by the light-guiding plate 121 so that the light is totally reflected inside the light-guiding plate 121, and second deflecting means 140 (for example, a multilayer structure in which a number of light-reflecting films are stacked) causing the light that has propagated with total reflection inside the light-guiding plate 121 to be output from the light-guiding plate 121.
There are other virtual-image display devices (image display devices) each employing hologram diffraction gratings so that an observer can observe a two-dimensional image formed by an image-forming device in the form of a virtual image enlarged by a virtual-image optical system, as disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2007-94175.
FIG. 10A is a conceptual diagram of an exemplary image display device 300. The image display device 300 basically includes the image-forming device 111 displaying an image, the collimating optical system 112, and an optical device (light-guiding means) 320 receiving light of the image displayed on the image-forming device 111 and guiding the light therethrough toward an eye 41 of an observer. The optical device 320 includes a light-guiding plate 321, and first and second diffraction grating members 330 and 340 provided on the light-guiding plate 321. The diffraction grating members 330 and 340 are reflective volume-hologram diffraction gratings. The collimating optical system 112 receives light emitted from the pixels of the image-forming device 111, collimates the light into parallel light, and outputs the parallel light toward the light-guiding plate 321. The parallel light enters and is output from a first surface 322 of the light-guiding plate 321. The first and second diffraction grating members 330 and 340 are provided on a second surface 323 of the light-guiding plate 321, the second surface 323 being parallel to the first surface 322.
In a head-mounted display (HMD) apparatus in which two image display devices are to be worn on the head of an observer, it is important that the distance between the two image display devices matches the distance between the eyes of the observer. The distance between the centers of the eyes varies between individuals, ranging from about 58 mm to about 72 mm, within a difference of about 14 mm. Accordingly, each of the two image display devices is desirably movable by about 7 mm in a first direction, which is a direction defined by a virtual line connecting the centers of the eyes of the observer. A direction perpendicular to the first direction, or a vertical direction with respect to the observer, is defined as a second direction.
Examples of such a binocular head-mounted image display apparatus including a mechanism configured to adjust the distance between right and left image display devices are disclosed in, for example, Japanese Unexamined Patent Application Publications No. 8-136853 and No. 8-136858